As everyone else has said, the FX55 was mighty, but its time is gone - it is an old chip, and that's why they're being discounted. The E6300 would be better.
Best bet, bang for buck, however is an Opteron 165 or Opteron 170 right now (available from NewEgg if they haven't run out yet)... around $150 to $170, and they overclock from 40 to 50% almost every one. Not as fast as the very top E6600/E6700 C2D, but a lot cheaper. You would be stuck with DDR memory, however, which while not a performance problem in the least, would limit future upgrades.